The invention relates generally to batch processing of semiconductor wafers using, for example, plasma etching or chemical vapor deposition. More particularly, the invention relates to a batch processing system wherein the pressure in the process reactor is cycled through varying pressures to improve the uniformity of such deposition and etch processes.
Semiconductor devices are constructed of patterned layers of electrically conductive, non-conductive and semi-conductive materials stacked over a silicon wafer. The layers of material are successively deposited on the wafer and etched into predefined patterns to form individual component structures within the particular device being fabricated. The manufacturing process often includes deposition and/or etch steps in which semiconductor wafers are processed in a group or xe2x80x9cbatch.xe2x80x9d Batch processing tools include barrel reactors, diffusion furnaces and the like, wherein each batch of wafers may be subjected to various chemical, mechanical or electrical processes.
The rate of production of conventional batch processing tools, such as those used for plasma etching and chemical vapor deposition, is often limited by the diffusion of reactant gases or reaction products to the center of the wafers. This is especially true in tube shaped reactors which hold a batch of wafers closely spaced and parallel to one another. In such conventional reactors, which are operated at a near constant pressure, the gaseous reactants and reaction products diffuse through the small space between the wafers. The diffusion of the reactants and reaction products to the center of the wafers is typically the slowest step in the deposition or etch process. In addition, the chemical and mechanical processes through which materials are deposited on or etched off the surfaces of a wafer occur more slowly at the center of the wafer than at the edge of the wafer. Therefore, the deposition or etch profile tends to be non-uniform across the surface of the wafer. That is, more material is deposited on or etched from the edge of the wafer than is deposited on or etched from the center of the wafer.
The present invention is directed to a novel batch processing system wherein the pressure in the reactor is cycled through a varying pressure to increase the transfer of the reactant materials to the center of the wafer. One object of the invention is to improve the uniformity across the surface of the wafer of the deposition or etch process carried out in batch processing tools. It is another object of the invention to increase the rate of transfer of the reactant materials to the center of the wafer and thereby increase throughput in batch processing systems.
These and other objects and advantages may be achieved by a method for improving uniformity in batch processing of semiconductor wafers that includes the steps of (i) feeding reactant gases into a reaction vessel, (ii) exhausting unused reactive gases and/or reaction by-products from the reaction vessel, and (iii) cycling the pressure in the reaction vessel between a higher pressure Phigh and a lower pressure Plow. Another version of the invention provides an apparatus for batch processing semiconductor wafers used, for example, in plasma etching and chemical vapor deposition. The apparatus comprises (i) a reaction vessel, (ii) a feed means for feeding reactive gases into the reaction vessel, (iii) an exhaust means for exhausting unused reactive gases and/or reaction by-products from the reaction vessel, and (iv) a pressure control means for cycling the pressure in the reaction vessel between a higher pressure Phigh and a lower pressure Plow.
In one aspect of the invention, the higher pressure Phigh is maintained for a predetermined period of time Thigh and the lower pressure Plow is maintained for a predetermined period of time Tlow. In one preferred version of the invention, wherein the method or apparatus is used in plasma etching, the higher pressure Phigh is in the range of 500 millitorr to 1500 millitorr, the lower pressure Plow is in the range of 200 millitorr to 400 millitorr, Thigh is in the range of 5 milliseconds to 50 milliseconds, and Tlow is in the range of 0 to 100 milliseconds. In a second preferred version of the invention, wherein the method or apparatus is used in chemical vapor deposition, the higher pressure Phigh is in the range of 100 millitorr to 500 millitorr, the lower pressure Plow is in the range of 50 millitorr to 500 millitorr, Thigh is in the range of 5 milliseconds to 50 milliseconds, and Tlow is in the range of 5 milliseconds to 200 milliseconds.